The present invention relates to a device and method for automatically hemming and seaming pre-cut workpieces such as sleeve blanks. In the preferred embodiment, the present invention includes a device and method for conveying the workpieces along a predetermined curve during seaming after the pre-cut workpiece has been hemmed, folded over and turned inside out. The invention also relates to maintaining control of the workpiece throughout subsequent sewing operations, such that predetermined stitch patterns are accurately followed.
In the manufacture of shirts, sleeve blanks are placed on an initial conveyor that carries the sleeve blank to a work station where an edge is trimmed and hemmed and then the blank is folded and turned inside out. When starting the hemming and folding operations the outer surface of the sleeve is facing up, while when performing the subsequent seaming operations the sleeve is folded inside out. A mechanism for folding and turning a sleeve blank inside out after it has been trimmed and hemmed is disclosed in U.S. Pat. No. 5,197,722, which patent is hereby included by reference as a part of this application. In this patent after an edge of the sleeve blank has been hemmed and the hemmed sleeve blank is being transported by the conveyor, the leading edge of the hemmed sleeve blank is recognized by a sensor. The sensor triggers a lifting apparatus which lifts the leading portion of the hemmed sleeve blank up and into a jaw. The jaw holds the leading portion of the hemmed sleeve blank stationary and a front air blower is actuated. The hemmed sleeve blank is folded in half and turned over as the conveyor continues to convey the remainder of the cloth underneath the jaw while the front air blower is exerting its force on the hemmed sleeve blank in the opposite direction. The jaw opens to release the leading portion of the hemmed sleeve blank and then the trailing edge of the hemmed sleeve blank passes a sensor which triggers a rear air blower. The rear air blower exerts its force in the direction of the conveyor movement and aligns the cloth and completes the fold.
In the prior art devices when the hemmed and folded sleeve blank reaches the distal end of the initial conveyor it is automatically picked up and deposited on a second work support surface for a seaming sewing machine that applies a seam to the workpiece as the workpiece is fed in a precise predetermined pattern. A hemming, folding and seaming machine for performing the above described operations is disclosed in U.S. Pat. No. 4,896,619, which patent is hereby included by reference as a part of this application.
In the above identified '619 patent, fabric sleeve blank is placed on one end of an initial conveyor by the machine operator. One edge of the fabric sleeve blanks are automatically hemmed by a sewing machine as they move along the initial conveyor. At the distal end of the initial conveyor the hemmed sleeve blanks are automatically picked up by a cloth pick-up device which folds the blanks and deposits them on either a second conveyor or a pickup table adjacent to the distal end of the conveyor. Various feed control mechanisms are disclosed for controlling the folded and hemmed sleeve blank as it is fed to the seaming sewing machine along a predetermined pattern that may include curves. Although the mechanisms disclosed in the '619 patent performs its intended function well, it does have limitations. For example, the machine operator loading the pre-cut sleeve blanks on the initial conveyor has adequate time to decrease the spacing between blanks by placing the blanks on the conveyor such that the edges overlap. This has the effect of increasing the output of the mechanism, and thus is a more efficient and economic procedure. However, when the blanks are placed on the initial conveyor with the edges overlapped, the overlapped edges interfere with each other where the cloth pick-up device attempts to pick up and fold the hemmed blanks. Furthermore, the various devices and methods used to control the folded sleeve blanks as they are fed to the seaming machine on the second conveyor are very expensive and complex, and require a large number of parts and assemblies. The prior art devices do not have sufficient control of the workpiece to automatically produce a seam that follows a predetermined curve or pattern. Still further, the prior art devices are limited in the length of seam that they can automatically produce and thus can not be used for longer sleeves. For these reasons a high productivity, lower cost device, that will hem, fold and produce a high quality seam, is needed. There is also a need for a machine that can produce a high quality sleeve that has a relative long length.